9.B.74 The Phage Infection Protein (PIP) Family

The PIP family includes large proteins with 1 N-terminal hydrophobic TMS, a hydrophilic domain of variable length, and 5 C-terminal putative TMSs. The functionally characterized protein from Lactococcus lactis is of 901 aas (Geller et al., 1993). Homologues obtained with one PSI-BLAST iteration include members of the MmpL family of the RND superfamily (e.g., a Bacillus protein, gi#89208076; 1038 aas). With poorer scores, a protein annotated as an ABC-2-like sequence (gi#89200681; 392 aas with 1 TMS followed by a 150 residue hydrophilic domain followed by a C-terminal 5 putative TMSs) was retrieved. Another protein annotated as ABC-2 was smaller with 6 putative TMSs in a 2 + 3 + 1 arrangement (gi#57234453; 241 aas).

The 5 TMS unit at the C-termini of all of these proteins comes up as ABC2-membrane, CO60842 and TagG in the conserved domain database (CDD). It also shows a partial Maf nucleotide-binding protein domain implicated in septum formation. The full-length 901 aa phage infection protein of Lactococcus lactis (P49022) is equivalent to COG1511. Its requirement for phage infection is described by Geller et al. (1993).